Ya, or they let the temps get that low because its winter and is hard to keep night time temps up.That's perfectly fine...you might wanna try to bump up the temp at night a lil more if you can...the ideal range to be in is 15 degrees. So if your day temp is 75F, 60F would be ok to dip to at night. I wouldn't worry about it though it's not gonna do any damage...some people prefer the cooler temps at night to get the "fake" blue or purple characteristic, but i say they do it to pretend they have some sorta cool strain...when infact they don't.
I live in a pretty cold inviroment...and i have no problems keeping my temps up. If it gets that cold...put a little space heater near the room and let the warm air makes your babies happy. Letting your plants drop too much in temp can cause it to stunt in growth.Ya, or they let the temps get that low because its winter and is hard to keep night time temps up.